The present invention relates to the field of telecommunications cables having optical fibers.
Optical fiber cables that include a plurality of optical fiber micromodules, each optical fiber micromodule being covered by a supporting sheath surrounding one or more fibers, are already known, in particular from documents FR-A-2 665 266 and FR-A-2 706 218.
In a known manner, a micromodule telecommunications cable has a plurality of optical fibers grouped together in micromodules within a (central) cavity that constitutes a core of the cable. The central cavity is surrounded by a sheath. A micromodule may contain about 1 to 24 fibers that are covered together in a supporting sheath that is flexible and fine to a greater or lesser extent. The supporting sheaths of micromodules and the coatings of optical fibers may be colored, numbered, or encoded so as to make it easier to identify the fibers in the cable, e.g. when performing a connection operation.
With the development of optical fiber telecommunications systems that extend as far as the subscriber, known under the acronyms FTTH for “fiber to the home” or FTTC for “fiber to the curb”, it is desirable to provide a large-capacity cable containing a large number of optical fibers that are grouped together in micronodules. Such cables must make it possible to access each micromodule individually in order to serve a given building. For this purpose, operators make a branch connection from the telecommunications cable, an opening is formed in the sheath of the cable and one or more fibers are extracted in order to deliver signals to a given optical system.
Document EP-A-1 052 533 describes a method of accessing one or more optical fibers in a cable in order to make a fiber branch connection to an optical system. Two cuts are formed in the sheath of the cable in order to create a first opening through which the fiber is cut and a second opening through which the cut fiber is pulled out in order to make a branch connection.
Document U.S. Pat. No. 6,134,363 describes a method of accessing one or more optical fibers arranged freely in a cable. The sheath of the cable is removed on either side of peripheral reinforcing elements over a certain length in order to create a window that gives access to the fibers.
WO 01/60265 (A1) recites a surgical snare including an elongate barrel having a distal end and a proximal end. A handle having holes which can accommodate the fingers of a surgeon, is connected to the proximal end of the barrel. The handle is connected to a rod that extends along a central bore of the elongate barrel. The handle can slide along a slot formed in a proximal end portion of the snare. Moving the handle towards the proximal end of the snare causes a loop of wire to be retracted into the central bore of the elongate barrel. The distal end of the snare consists of a flattened, widened portion which has two cutting edges. The cutting edges can be used in conjunction with the loop of wire to assist in dissection of tissue. The snare may also include a vacuum port for removing smoke and blood from the site of the operation. The snare can be an electrosurgery snare.
The above surgical snare is however not suited for cutting an optical fibre, especially one such fibre arranged freely in a telecommunication cable. Further, the surgical snare is not formed around an object.
WO 98/30156 (A1) recites a graft being inserted into a passageway such as a patient's artery. After the distal end of the graft is tacked to the passageway, a special intraluminal cutting device is threaded along the graft and actuated at the appropriate position so that the graft can be cut to the proper size.
The above graft is however not suited for cutting an optical fibre, especially one such fibre arranged freely in a telecommunication cable. Further, the surgical snare is not formed around an object.
US 2005/209624 (A1) recites a surgical scissors includes two cutting blades operable via a handle. One of the blades is provided with a distally projecting needle-like tip which can easily pierce tissue. In use, the tip on the blade is gently pressed against a vessel, preferably at a shallow angle relative to the vessel, to define an entry hole. This shallow angle approach with the needle-like piercing tip reduces the opportunity for inadvertent puncture. The lower blade is then pushed further through the entry hole in alignment with the piercing tip such that the cutting blade portion of the lower blade also enters the vessel. The handle is then operated to cause the blades cut the vessel tissue there between to create the incision. The instrument facilitates making lengthwise incisions in vessels by eliminating offline cutting, and substantially reducing the likelihood of cutting the posterior vessel wall.
The above scissors are however not suited for cutting an optical fibre, especially one such fibre arranged freely in a telecommunication cable. Further, the scissors are not adapted to form a snare around an object.
WO 2008/008115 (A2) recites fiber optic distribution cables and methods for manufacturing the same are disclosed. The fiber optic distribution cables present one or more optical fibers outward of the protective covering for distribution of the same toward the subscriber. In one fiber optic distribution cable, a length of distribution optical fiber that is removed from the distribution cable and presented outward of the protective covering is longer than the opening at access location. In another embodiment, a demarcation point is provided for inhibiting the movement (i.e., pistoning) of the distribution optical fiber into and out of the distribution cable. In still another embodiment, an indexing tube is provided for indexing a tether tube within the indexing tube for providing the distribution optical fiber with a suitable excess fiber length. Additionally, other embodiments may include a fiber optic distribution cable having a dry construction and/or a non-round cross-section.
The cutting tool recited in the above document does not comprise a tube.
With the development of FTTH or FTTC, telecommunications operators are faced with a large increase in the number of connection operations that need to be performed on a given cable and at a given branch connection point. Thus, by way of example, after making an access window in order to connect a first subscriber, the operator may need over time to open that window again in order to extract another fiber so as to connect a new subscriber.
The methods and the tools described in some of the above-mentioned documents provide for opening two access windows, a first window for cutting one or more fibers, and a second window for pulling out the fiber(s) for making the branch connection. During a connection operation, it would be desirable to open only one window.
Document WO-A-2008/008115 proposes a method of distributing fibers from a cable by providing an installation that includes a tether for the excess length of extracted fiber. That document also describes a tool that can be used for cutting one or more fibers in the cable. The tool provides a tongue having an opening at one of its ends for passing a sharp filament that forms a snare around the fiber(s) for cutting. The tongue, with the snare, is inserted into the cable through an opening in the sheath and is slid along inside the cavity of the cable to the cutting point. The sectioned fiber(s) is then pulled out through the opening and arranged in the tether.
The tool described in that document allows only a relatively short length of fiber (175 millimeters (mm)) to be extracted for connection to the tether positioned on the sheath of the cable. A secondary cable must then be provided for connecting the extracted fiber to a subscriber optical unit. Furthermore, the sharp filament of the tool described in that document is merely guided by the tongue, without being protected; it might catch and damage fibers and/or other elements of the cable, in particular when the packing ratio of the cable is high.
There thus exists a need for a method of making a branch connection and for a tool that enables fibers to be sectioned at a considerable distance from a single opening, but without running the risk of damaging elements of the cable.